• If you ever spot Spam (either in the forums, or received via forum direct message) please use the Report button at the bottom of each post to make sure a Moderator can handle it quickly. Thanks for your help in keeping things running smoothly!

Should my Roksan amp keep blowing?

Hermoder

Member
Nov 21, 2019
4
0
20
I have a Roksan Blak amplifier. Had it for three months but it has been back to Roksan twice for repair as the left channel keeps blowing. The amp is capable of 150w per channel and is powering PMC 23 speakers that have a 150w capacity, and I set the volume at 40. It is capable of going to 60. However Roksan have suggested I am playing the amp too loud. Anyone got any thoughts?
Ta, Mike
 

abacus

Well-known member
Sep 24, 2008
401
158
19,070
Check your speaker cables on the left channel for any stray strands, also its quite possible that there is a fault with the left speaker as you don't seem to have any problems with the right channel.

Bill
 
  • Like
Reactions: shadders

Hermoder

Member
Nov 21, 2019
4
0
20
Thanks Bill. I use Chord Clearway cables pre-terminated with banana plugs. Definitely no stray strands:). And the speakers were taken back to the retailer on two occasions for cheking and they could find no fault with either of them
Mike
 

Al ears

Moderator
Thanks Bill. I use Chord Clearway cables pre-terminated with banana plugs. Definitely no stray strands:). And the speakers were taken back to the retailer on two occasions for cheking and they could find no fault with either of them
Mike
In that case I would be asking Quad to replace the amp as unfit for purpose as it should be able to drive those speakers at full output without issue.
 

Gray

Well-known member
Nov 27, 2015
1,007
631
6,070
In that case I would be asking Quad to replace the amp as unfit for purpose as it should be able to drive those speakers at full output without issue.
You could ask Quad, but they'd probably refuse as the amp's a Roksan :)
Seriously though, imagine a glossy advert from an amp manufacturer with an asterisk:
*As long as you don't play it too loud.
(As has been said too, funny how it's always the left channel that suffers when 'too loud')
Give Roksan the opportunity to consider providing you with a replacement.
Any trouble, show them this thread - and see if they reflect on their 'too loud' verdict.
 
Last edited:

shadders

Well-known member
Nov 19, 2009
152
88
18,670
Hi,
Do you have an alternative amplifier to test at the same sound level to see if it struggles or other ? Have you changed the speakers around to see if the right channel is affected ?

The PMC 23 (from internet search) seem to be an easy load, so i doubt that it is the current drawn causing the issue.

When you state the left channel blown - what actually happens ?

Regards,
Shadders.
 

Hermoder

Member
Nov 21, 2019
4
0
20
Hi Shadders
The amp showedfive bars on the display. That, according to the manual, indicated a speaker or cable issue. Returned the amp to Roksan. Received back today with new motherboard. Connected it all up and now discovered that the left hand speaker midrange unit has burnt out. Speaker is now with dealer for repair.
As suggested, I have tried swopping amp speaker outputs around, bought new speaker leads and tested the speakers with a Sony AV amp without issue
 

shadders

Well-known member
Nov 19, 2009
152
88
18,670
Hi,
Sorry to hear that the mid-range driver has burned out. It is possible that the amplifier fault caused the burn out, and then repaired amplifier has no issues (obviously since it is repaired) and then you have to replace the mid range driver.

I checked the PMC 23 from the internet - is this not a 2 way design and the mid range is effectively the mid-bass unit ?

It is hard to tell what the issue was - so, it could have been a slightly defective mid range unit, which caused the amplifier fault, and also blew the driver.

Regards,
Shadders.
 

Hermoder

Member
Nov 21, 2019
4
0
20
Hi Shadders
Thanks for your interest. The PMC 23 has a midrange unit and bass reflex. The good news is that the dealer can replace the midrange for £165 incl. A lot cheaper than I was expecting. They expect to get it back to me early next week. I'm hoping that is the end of it:-(
Mike
 

Gray

Well-known member
Nov 27, 2015
1,007
631
6,070
Blimey Mike, that's an unfortunate sequence of events, which has added a bit of complication. There would seem to be only those 2 possibilities that shadders has pointed out.
In view of its repeated failures, my money would be on the amp being the cause of trouble.
It's true to say that not everyone runs their amp at two thirds of its output, you're pushing it a bit, but it should be up to it.
You can't really tell the cause by how it sounded - any distortion could have been the result of clipping amp and / or overheating driver voice coil.
You will presumably be mentioning the speaker driver burnout to Roksan (as £165 is not cheap).
Let's hope that all will be well for you eventually.
 
Last edited:
  • Like
Reactions: Squall Leonhart

chris661

Well-known member
Oct 30, 2019
191
117
270
Hi Shadders
The amp showedfive bars on the display. That, according to the manual, indicated a speaker or cable issue. Returned the amp to Roksan. Received back today with new motherboard. Connected it all up and now discovered that the left hand speaker midrange unit has burnt out. Speaker is now with dealer for repair.
As suggested, I have tried swopping amp speaker outputs around, bought new speaker leads and tested the speakers with a Sony AV amp without issue
When speakers burn out, they can often present a short-circuit to the amplifier. That can be the driver itself going short, or, if the driver goes open-circuit, the (effectively unloaded) crossover can present short circuits and weird phase angles.

The amplifier will try to drive those short-circuits, meaning it'll try to pass the hundreds of amps required. Of course, that much current is in the realm of very large high power amplifiers (I know this because I have a few of them - read up on the Crown MA12000i for example). A HiFi amp attempting that sort of current will fail, usually taking out the output transistors, probably driver transistors, maybe some PSU bits and pieces and anything else in-line with the speaker output.

Another point to consider is that the position of the volume control means almost nothing. If I connect my laptop to my HiFi, I can have the amp turned all the way up to 11, and then bring the volume down at the source and get perfectly sensible levels. Alternatively, I can connect up a professional mixing desk capable of +22dBU (10V RMS) output and barely have to turn the amp up at all to get maximum output.

It seems to me that you're asking too much volume from this particular setup. I looked up the PMC 23 speakers, and they're a floorstanding 5" 2-way speaker. They're never going to move loads of air or get particularly loud - I would strongly suggest that you replace them with higher sensitivity and more power handling. I'd go for either a pair of 6"s or an 8" midbass driver. More, if you can afford the space.

Hope that helps to dispel some mysteries.

Chris
 

Al ears

Moderator
You could ask Quad, but they'd probably refuse as the amp's a Roksan :)
Seriously though, imagine a glossy advert from an amp manufacturer with an asterisk:
*As long as you don't play it too loud.
(As has been said too, funny how it's always the left channel that suffers when 'too loud')
Give Roksan the opportunity to consider providing you with a replacement.
Any trouble, show them this thread - and see if they reflect on their 'too loud' verdict.
Good point, no idea why I wrote Quad. Wishful thinking?? :)
 

millennia_one

Well-known member
Sep 1, 2014
378
150
11,070
I think it’s just a case your treating the system a bit rough. Not all Amps are designed to use there full volume rotation even though some have suggested they should. My Sugden can only use about a quarter of its rotation before it’s at full volume anything after that and it will start to distort.

In the past I found when using the pmc 2023’s they require juice to get them going but they don’t like play excessively for too long. It’s a only little cone being asked to do a lot everything has there limits. Tbh your lucky they are repairing it, the engineers will be able to tell it being over driven.
 
I think it’s just a case your treating the system a bit rough. Not all Amps are designed to use there full volume rotation even though some have suggested they should. My Sugden can only use about a quarter of its rotation before it’s at full volume anything after that and it will start to distort.
The volume controls on Roksan amps, I believe, we’re designed to be used above the 12 o’clock position.
 

shadders

Well-known member
Nov 19, 2009
152
88
18,670
? There's not much point in an amp that cannot operate over the full range of it's volume control, or am I missing something here?
Hi,
The ideal situation is where the signal from the source (CD Player for example) with the peak program material causes the amplifier to be just below clipping with the volume control at the maximum position.

All that seems to be happening with the posters system, is that the source has a higher output voltage than designed for the Roksan amplifier, so it outputs a higher volume into the loudspeaker with the volume control setting lower.

You can get cables with attenuation inbuilt - such that these will reduce the signal voltage from the source, and allow the user to use more of the volume control range. This may be beneficial in that at low volumes, the balance of a stereo potentiometer is much worse (tracking error). Implementing the attenuating cables will reduce the error.

Regards,
Shadders.
 
  • Like
Reactions: gasolin
? There's not much point in an amp that cannot operate over the full range of it's volume control, or am I missing something here?
Most amplifiers reach their maximum output around the 12 o’clock Region with a normal 2 volt output from the likes of a CD player or other normal sources. Turntables have lower out though, and the remaining gain left after that 12 o’clock point is handy for this (and lower sensitivity loudspeakers).
 

DougK

Well-known member
Dec 8, 2013
766
458
11,270
Most amplifiers reach their maximum output around the 12 o’clock Region with a normal 2 volt output from the likes of a CD player or other normal sources. Turntables have lower out though, and the remaining gain left after that 12 o’clock point is handy for this (and lower sensitivity loudspeakers).
My Marantz is like this but it is one of many brands out out there that are similar, by 12 o'clock it's painfully loud, go any further and you're into the realms of distortion and clipping. This is why I fitted Rothwell passive attenuators to all inputs except the phono stage. I now get a much larger usable sweep on the volume knob before it becomes stupidly loud.
 

gasolin

Well-known member
Mar 17, 2013
732
118
19,070
Some amps with normal volume knob 200mv input sensitivity will already play loud at 9 o'clock from a cdplayer, distortion a 10 o'clock, distorted as hell at 11 o'clock.

I don't know how your amp is but it might already reach it's max power at max 30 when playing cd's.

Ideally it would be max power at 45-50 out of 60 with music recorded as loud as possible (peak level) without distortion, because then you still would have some extra gain you can use when playing music that is not recorded as loud as possible when peaking with no distortion, typical that is 0db peak level.
 
Last edited:
  • Like
Reactions: shadders

chris661

Well-known member
Oct 30, 2019
191
117
270
Most amplifiers reach their maximum output around the 12 o’clock Region with a normal 2 volt output from the likes of a CD player or other normal sources. Turntables have lower out though, and the remaining gain left after that 12 o’clock point is handy for this (and lower sensitivity loudspeakers).
The amplifier doesn't care about the sensitivity of the speakers - it'll still clip.

I've measured my CXA80, and found that when I feed it from the USB input, it can be made to clip at the very end of the volume control's travel. ie, exactly as it should be.

That's with a digital input, though.

When it comes to analogue inputs, it's all down to gain structure. My previous post on this thread gives a hint about that, but there's lots more reading to be done if you search that term online. Most of it will reference professional applications, but the concepts apply to home HiFi, too.

Chris
 

ASK THE COMMUNITY

TRENDING THREADS

Latest posts